This invention relates generally to a rupture disc assembly to vent pressure from an inflatable system. Particularly, the invention relates to a rupture disc assembly for use with pneumatic pipeline plugs to vent air at a predetermined internal plug pressure to thereby prevent overinflation of the pneumatic plug.
Pneumatic plugs are constructed to be inflated to a desired pressure and any undue excess pressure may cause damage to the plug and cause possible injury to the user and surroundings. A long felt need exists in the pipe plug art to relieve excess pressure at a specified pressure reading. In the past, the alternatives have primarily been read-back pressure gauges and pressure relief valves, however, both the reliance on pressure gauges and on pressure relief valves have not been adequate.
Read back pressure gauges are typically not sufficient because they may be broken and/or out of calibration and do not inherently prevent over inflation. Read back gauges also require operator intervention and therefore, are limited in their effectiveness to prevent pneumatic plug overinflation.
Pressure relief valves have also been found to not be particularly suited for pneumatic pipe plug applications because they typically were unable to bypass sufficient fluid flow once they start to open. One reason for this is that the spring-loaded steel ball used to seal the valve unit blocks the air flow once it starts to open, thus, drastically reducing the air flow for a given orifice diameter. The pressure relief valve, therefore, does not effectively allow large airflows until high pressure differentials are achieved, i.e., the steel ball is completely pushed out of the way of the air flow. There is a need to bypass large flow values at low pressure differentials as opposed to high pressure differentials.
A further reason pressure relief valves are not suitable for use in inflatable pipe plugs is that such relief valves are subject to leakage due to contamination of the valve seal. The application of using inflatable plugs is often very dirty and debris is very likely to get into the sealing area and cause the valve to leak slowly, ultimately causing the plug to dislodge from the pipeline, and potentially causing damage and injury. Thus, a need exists in the pneumatic pipeline sealing plug art to provide a reliable means to prevent over inflation.
The rupture disc assembly of the present invention prevents overinflation of inflatable sewer plugs by utilizing a disc or like structure that is constructed to rupture at a specified pressure which is below the ultimate burst pressure of the plug. The resultant opening in the ruptured disc and holder structure is of sufficient size to bypass the air coming from the compressor used to inflate the plug so that the ultimate burst pressure of the plug is not reached.
The utilization of a rupture disc assembly overcomes the shortcomings of the pressure relief valves of the prior art. When the disc ruptures, the large orifice created is capable to bypass large quantities of air much more efficiently than a pressure relief valve.
Applicants' assignee is the owner by assignment of copending U.S. patent application Ser. No. 11/103,084, filed on Apr. 11, 2005, now U.S. Pat. No. 7,325,574, issued on Feb. 5, 2008 for a rupture disc assembly which is incorporated by reference herinto.
The rupture disc holders of the present invention may be constructed and arranged to be mounted on either the inside or outside of the pneumatic plug body structure. The rupture disc holder may, for example, be mounted on the outside of a pneumatic plug and may be adapted to be threadingly mounted to the end plate of the pneumatic plug structure or to a threaded structure mounted to the end plate to provide servicing access. The rupture disc structure may also be incorporated into the structure of the end plate or to a structure that may be mounted to the end plate and which is in communication with the pneumatic plug.